Addendum: I lied at first about how to get thin from gluttony, maybe (4)
I believe the answer is:
lisp
'to get thin from gluttony maybe' is the definition.
I can't judge whether this definition defines the answer.
'addendum i lied at first about' is the wordplay.
'addendum i' becomes 'psi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at first' suggests taking the first letters.
'about' is a reversal indicator.
The first letter of 'lied' is 'l'.
'psi'+'l'='psil'
'psil' backwards is 'LISP'.
'how' acts as a link.
Can you help me to learn more?
(Other definitions for lisp that I've seen before include "peech impediment" , "Thpeak like thith" , "Be unable to pronounce S" , "Have difficulty pronouncing `s'" , "Talk like thith" .)